Temperature sensing assembly for a thermo-switch



TEMPERATURE SENSING ASSEMBLY FOR A THERMO-rSWITCI-I Original Filed Feb. 17. 1961 ll IO 7 INVENTOR. 32 38 EDWARDG THEM as FIG. 5 L.

ATTORNEY United States Patent F 3 155,798 TEMPERATURE SEbISlNG ASSEMBLY FGR A THERMQ-SWITEH Edward G. Them, Mansfield, Ohio, assignor to Therm-@- Disc, incorporated, Mansfield, Ohio, a corporation oi Ghio Qriginal application Feb. 17, 1961, Ser. No. 9tl,il21 new Patent No. 3,13d,tltl3, dated May 19, 1954-. Divided and this application Feb. 27, 1962, Ser. No. 176,016

3 Claims. (Cl. 260-137) This invention relates to an improved heat responsive switch, and more particularly to switch actuating means embodying a heat sensitive probe member adapted to be positioned in the fuel flame of heating appliances such as furnaces, ranges, and clothes driers.

This application is a division of my co-pending application Serial No. 90,021, filed February 17, 1961, now US. Patent No. 3,134,003, issued May 19, 1964.

Various types of switches have been proposed heretofore which are intended to operate in response to the presence or absence of a gas frame in heating appliances such as furnaces, cooking ranges or ovens, and clothes driers. Such switches have embodied many undesirable features and drawbacks, and through failure have proved to be unsafe "for domestic use as safety devices in such appliances. For example, in devices in which a probe has been used as a flame sensing element, after extended periods of exposure to the flame, the probe will deteriorate and disintegrate or break, and thus fail to actuate the switch in the electric circuit of the valve controlling t" flow of gas to the appliance. In other cases, the probe will change in physical character to the extent that the switch will fail to operate within a predetermined prescribed period of time or Within desired temperature limits. in devices using bi-metal as a flame sensing element, over-stress and deterioration of the bi-metal are efiective to cause failure of the switch actuating elements of the device or to cause the switch to operate within unsafe limits.

It is among the objects of the present invention to pro vide a new and novel temperature sensing assembly for actuating a switch controlling the electric circuit to an electrically operated fuel valve which is adapted to interrupt or open said electric circuit on the absence or re moval of a flame impinging on the sensing device or upon a substantial drop in the temperature surrounding the same.

Another object of the present invention is to provide a switch actuating device which will operate within fixed limits or" time or temperature regardless of physical changes in the character of the flame sensin element upon extended periods of exposure to .a flame.

A still further object of the invention is to provide a switch for controlling the flow of current to an electrically operated fuel valve which is actuated by a flame sensing element, wherein the switch elements are caused to open or close in the event of failure of the flame sensing element.

It is a still further object of the invention to provide a switch for a heating appliance which because of its simplicity, economy of construction and reliability and elliciency of operation is particularly well suited as a protec tive device in controlling the circuit to the fuel valve of such heating appliance.

Another object of the invention is to provide a probe type flame sensing element for a switch wherein relative movement of the members of the sensing elements is coordinated with the spacing of the contact elements of the switch so that the former is positive in the switch actuating movemen within predetermined limits.

' These and other objects and advantageous features of chamber l2.

Fat-un ted Nov. 3, i964 the invention, not at this time more particularly pointed out, will become apparent as the nature of the invention is better understood from the following deailed description taken in conjunction with the accompanying drawing, wherein like reference charctcrs denote corresponding'paits and wherein:

FIGURE 1 is top plan view of a device made in accordance with the present invention;

FIGURE 2 is a longitudinal section view taken along the line 2-2 of FIGURE 1 with the switch contacts shown in open position;

FIGURE 3 is a vertica sectional view taken along the line 3--3 of FIGURE 5, centrally through the switch mechanism;

FIGURE 4, is a sectional view taken along the line i4 of FlGURE 2; and

FIGURE 5 is a sectional View similar to FIGURE 2 showing the contacts of the switch in closed position.

With reference to FIGURE 2 of the drawing in its overall assembly, the switch device of the present invention embodies a switch proper A, which includes at least one fixed contact and a movable contact which is adapted to either engage or disengage from the fixed contact, a dame sensitive assembly B, and a movement limiting assembly C which coordinates the movement of the elements of assembly B in response to the presence or absence of a flame projecting on the latter or the influence of substantial temperature changes thereon. in accordance with the present invention the switch proper A and the temperature sensing assembly B in themselves are of conventional construction. The elements of C coordinating the movement of the elements of assembly B to actuate the contact elements of switch A constitute a novel and improved arrangement for translating the movement which takes place in the assembly B in response to the absence of a flame within the chamber surrounding assembly B and for imparting such movement for positive action of the switch proper.

The switch A which, as stated is of conventional structure, is embodied within a housing it) which may be of suitable insulating material, although under certain applications of the device it may be desired to construct the housing of material which would withstand extremely high temperatures, such being the case when the switch would be placed in close proximity to either the pilot flame or main burner of a heating appliance. The housing it is generally cupshaped having a closed upper end as shown in FlGURES 2, 3 and 5 and at its lower end presenting a laterally outwardly protruding peripheral flange 11. As shown in the drawing the housing 10 presents a generally cylindrical downwardly facing switch The switch housing it is supported by a cup-shaped metal case 13, with its bottom wall 14 secured to a metal mounting bracket 15 which is adapted to be assembled on the appliance with which the device is used and may take any suitable form varying with the application of the device. The metal case 13 has a generally cylindrical side wall 15 which extends upwardly from the bottom wall 14 and terminates in a laterally inturned flange l7 snugly overlying the peripherally upwardly facing shoulder of the flange 11 formed on the switch housing it Between its outturned wall portion 18 and its inturned flange 17, the metal case 13 snugly engages the periphery of flange ill and seats against the bottom thereof.

Mounted within the switch chamber 12 is a stationary switch contact member 19 having disposed thereon a rounded contact surface 26. This stationary contact member has a horizontal portion which projects from the wall into the switch chamber and has an upwardly extending stem which passes through the housing wall for connection to a terminal 22 disposed outside of the switch housing. Mounted on the exterior of housing in diametrically opposed to the terminal 22 is a second terminal 23 secured to the end of a supporting arm 24 which extends through and depends from the top wall of the housing within the switch chamber and has an inturned portion 25 formed on the lower end thereof. Mounted on the portion 25 by means of rivet 26 is a cantilever contact-carrying arm 27 which supports at its outer free end a contact button 28 adapted to engage the stationary contact button 29. The \arm 27 is provided with a centrally disposed opening 29 therethrough adapted to receive the shank portion 3t) of a headed ceramic pin 31. The shank portion 3% is of sufiicient length to extend into the chamber 12a defined by the metal case 13 and is arranged to move with the mobile contact carrying arm 27.

The temperature sensing assembly in the present invention comprises an elongated tube 32 having a flange 33 formed on the upper end thereof and arranged to seat within a recess 34 formed in the mounting bracket 15. An elongated rod 35 is welded into the lower end of the tube 32 as at 36 and extends upwardly therefrom through the tube 32 in concentric relation therewith. The rod 35 projects loosely through a central bore 37 formed in plate 33 secured on the inner face of bottom wall 14 of the casing H by means of rivets 39 extending through the casing wall 14 and mounting bracket 15. The flanged end 33 of the tube 32 is thus securely clamped between the upper face of the mounting bracket and the outside surface of the bottom wall 14 of the case 13. The upper end of the rod 35 is disposed in the chamber 12a of the switch case 13. Preferably the rod 35 is of a metal having a relatively low coefficient of expansion while the tube 32 may be of any suitable metal that has an appreciably higher coefiicient of expansion than the rod 35. With this arrangement, which is a conventional structure of controls of this general design, when the temperature sensing assembly is heated, the inner rod 35 will expand less than the outer tube 32, and the upper end of the rod 35 will withdraw from within the chamber 12a.

In accordance with the present invention, the relative mevernent of the rod 35 with respect to the tube 32 is translated to the switch contacts by the element of assembly C and when such movement exceeds a predetermined amount, assembly C is effective to control the same; or if perchance, the elements of the assembly B become so deteriorated or separated that the assembly fails to function normally, the assembly C Will come into play to effectively actuate the contacts of the switch 11A?! Mounted on the upper end of rod 35 is a substantially rectangular spring member 40, the bottom wall thereof being riveted to the rod 35 as at 4-1. The upwardly extending side walls 42 and 43 of the spring member 4-0 are biased toward each other and the free ends thereof are turned inwardly to form gripping jaws 44 and 45 which terminate in edge portions having opposed semicircular recesses to receive and grip therebetween the shank portion 30 of the pin 31.

The top wall portion 46 of the housing ill; is apertured to receive an internally threaded bushing 47 which receives an adjusting screw 43 the outer end of which is slotted to receive a suitable tool.

In the operation of the device, as shown in FIGURE 2, the switch contacts and elements of assembly C are shown in the position under normal room temperature. The space gap between the fixed contact 20 and the mobile contact 28 has been predetermined and adjusted by means of the projectig screw 4%. The mobile contact arm 27 being biased upwardly the switch is normally open. Upon heat being applied to the heat sensitive tube 32 or when the same is introduced into an atmosphere of higher temperature, expansion of tube 32 withdraws the rod 35 from the chamber 12a. The spring member dt mounted on the end of the rod 35 grips the shank of pin 31 with sufficient force to move the same downwardly as viewed in FIGURE 2 against upward bias of the mobile contact carrying arm 27 to close the switch contacts 2t) and 28 as shown in FIGURE 5. Upon continued withdrawal movement of the rod 35 after the contacts have been closed, the clamping surfaces 44 and 45 of the spring member 40 will slide along the shank 39 of pin 31. Thus the linkage between the ternpenature sensitive element and switch elements is placed in position to effectively open the switch contacts upon a relatively small drop in temperature as sensed by the probe. Upon such a drop in temperature the tube 32 will contract moving the rod 35 into the chamber 12a along with the spring member 4%. The gripping force of the jaws 44 and 45 on the shank of pin 31 will translate the movement of the rod to pin 31 and such movement together with the bias of the contact carrying arm 27 will open the switch contacts promptly. It is to be noted that the switch elements will open under relatively low temperature conditions as well as high temperature, any movement of the rod being positively translated to the switch. Continued movement of the rod will cause the upper surface of the head of the pin 31 to engage the lower end of the adjusting screw 48, which has been previously adjusted to fix the spacing between the contacts 2t? and 28. Upon such contact between the pin 31 and adjusting screw 48 further movement of the rod 35 is permitted by the sliding of the jaws of spring member 40 along the shank 3h of the pin. In case of a separation of rod 35 and tube 32 due to deterioration thus releasing the rod for free movement within the chamber 12a, the bias of contact carrying arm 27 will immediately open the contacts.

In the normal use of heat sensing elements comprising assembly B, continued impingement on the tube 3.2 of a flame will be effective to change the physical character of the elements of the assembly, such as, for example, there is a tendency due to what is known as carbon growth for the tube to be permanently elongated. Such elongation of the tube would be taken up in the slippage of the clamping jaws of the spring member with respect to the shank of the ceramic pin, thus there is always relative movement upon the flame being removed from the tube or where the temperature is substantially decreased in the area surrounding the tube and the contraction would be effective to cause the rod to move into the chamber 12a and separate the contacts. In other insances the continual impingement of the gas flame upon the tube causes deterioration of the tube member and eventually brings about a condition where the tube and rod separate. Under such condition, the bias of mobile contact carrying arm 27 being free of any restraint by the rod will be effective to separate the mobile and fixed contacts of the switch A. Thus, upon the absence of a flame or upon a breakage of the elements of the temperature sensing assembly B or the ineffeo tiveness of the elements thereof to actuate the switch, assembly C functions to permit the contacts of the switch to open.

While there has been described and herein illustrated in the accompanying dnawing a preferred embodiment of the present invention, it is to be understood that various modifications, omissions, and refinements which depart from the disclosed embodiment may be adopted without departing from the spirit or scope of this invention as defined in the appended claims.

I claim:

1. In a thermo-switch for controlling a flame, a housing defining a switch chamber, a pair of electrical terminals mounted on said housing, switch elements mounted in said chamber including a stationary contact connected to one terminal, and a mobile contact connected to the other terminal, a cantilever arm of electrically conductive material supporting said mobile contact for conductin" an electric current between said terminal, said cantilever arm comprising spring means biasing said mobile contact in one direction to open the switch, means for limiting the movement of said arm in said one direction and for adjusting the maximum spacing of said contacts, a flame sensing probe extending outwardly from said housing in the opposite direction, said probe comprising an elongated tube mounted on said housing and extending away from said switch chamber and a metal rod mounted in said tube and connected to the outer end of said tube, said rod being formed of a metal having a coefficient of expansion lower than that of said tube and having a length greater than that of said tube, the free end portion of said rod projecting into said switch chamber, and means for connecting said rod to said cantilever arm to close said switch in response to heating of said probe comprising a pin of ceramic insulating material and a U-shaped spring member having side Walls that are biased toward each other, said pin being connected to said arm and extending toward said r-od between said side Walls, said U-shaped spring member being connected to the free end portion of said rod between said side walls and having inturned jaws providing means for gripping the opposite sides of said pin to effect closing of said switch in response to axial movement of said rod and for sliding axially on said pin when the pin is 6 positioned in either extremity of its path of movement, whereby said flame sensing probe remains sensitive to smali decreases in temperature, said spring means opening said contacts upon separation of said rod and said tube to indicate deterioration of said probe.

2. A flame-sensing thermo-switch \as defined in claim 1 herein intermediate portion of said arm has opening to receive said ceramic pin, said pin has an enlarged read engaging the face of said arm remote from said rod and a cylindrical portion engaging said jaws, and said jaws have opposed semi-circuiar recesses to receive and grip said cylindrical portion.

3. A flame-sensing thermo-switch as defined in claim 2 wherein the means for limiting movement of said arm comprises an adjusting screw carr'ed by said housing for the enlarged head of said ceramic pin.

References Cited in the file of this patent UNITED STATES PATENTS 2,195,649 Hallenbeck et al. Apr. 2, 1940 2,996,716 Butts July 4, 1961 3,029,329 Boleslty Apr. 10, 1962 FOREIGN PATENTS 431,798 Great Britain July 16, 1935 

1. IN A THERMO-SWITCH FOR CONTROLLING A FLAME, A HOUSING DEFINING A SWITCH CHAMBER, A PAIR OF ELECTRICAL TERMINALS MOUNTED ON SAID HOUSING, SWITCH ELEMENTS MOUNTED IN SAID CHAMBER INCLUDING A STATIONARY CONTACT CONNECTED TO ONE TERMINAL, AND A MOBILE CONTACT CONNECTED TO THE OTHER TERMINAL, A CANTILEVER ARM OF ELECTRICALLY CONDUCTIVE MATERIAL SUPPORTING SAID MOBILE CONTACT FOR CONDUCTING AN ELECTRIC CURRENT BETWEEN SAID TERMINAL, SAID CANTILEVER ARM COMPRISING SPRING MEANS BIASING SAID MOBILE CONTACT IN ONE DIRECTION TO OPEN THE SWITCH, MEANS FOR LIMITING THE MOVEMENT OF SAID ARM IN SAID ONE DIRECTION AND FOR ADJUSTING THE MAXIMUM SPACING OF SAID CONTACTS, A FLAME SENSING PROBE EXTENDING OUTWARDLY FROM SAID HOUSING IN THE OPPOSITE DIRECTION, SAID PROBE COMPRISING AN ELONGATED TUBE MOUNTED ON SAID HOUSING AND EXTENDING AWAY FROM SAID SWITCH CHAMBER AND A METAL ROD MOUNTED IN SAID TUBE AND CONNECTED TO THE OUTER END OF SAID TUBE, SAID ROD BEING FORMED OF A METAL HAVING A COEFFICIENT OF EXPANSION LOWER THAN THAT OF SAID TUBE AND HAVING A LENGTH GREATER THAN THAT OF SAID TUBE, THE FREE END PORTION OF SAID ROD PROJECTING INTO SAID SWITCH CHAMBER, AND MEANS FOR CONNECTING SAID ROD TO SAID CANTILEVER ARM TO CLOSE SAID SWITCH IN RESPONSE TO HEATING OF SAID PROBE COMPRISING A PIN OF CERAMIC INSULATING MATERIAL AND A U-SHAPED SPRING MEMBER HAVING SIDE WALLS THAT ARE BIASED TOWARD EACH OTHER, SAID PIN BEING CONNECTED TO SAID ARM AND EXTENDING TOWARD SAID ROD BETWEEN SAID SIDE WALLS, SAID U-SHAPED SPRING MEMBER BEING CONNECTED TO THE FREE END PORTION OF SAID ROD BETWEEN SAID SIDE WALLS AND HAVING INTURNED JAWS PROVIDING MEANS FOR GRIPPING THE OPPOSITE SIDES OF SAID PIN TO EFFECT CLOSING OF SAID SWITCH IN RESPONSE TO AXIAL MOVEMENT OF SAID ROD AND FOR SLIDING AXIALLY ON SAID PIN WHEN THE PIN IS POSITIONED IN EITHER EXTREMITY OF ITS PATH OF MOVEMENT, WHEREBY SAID FLAME SENSING PROBE REMAINS SENSITIVE TO SMALL DECREASES IN TEMPERATURE, SAID SPRING MEANS OPENING SAID CONTACTS UPON SEPARATION OF SAID ROD AND SAID TUBE TO INDICATE DETERIORATION OF SAID PROBE. 